The invention relates to the provision of a straining assembly in a vessel for the treatment of pulp or the like. In continuous process treatment of cellulose for producing pulp, apparatus is provided at various stages (i.e. bleaching and washing) of the treatment for introducing a treatment liquid axially into the pulp, and then immediately thereafter removing the treatment liquid from the pulp after it has been spent. Conventional apparatus for this treatment is shown in U.S. Pat. Nos. 3,348,390, 3,372,087, 3,563,891, 3,599,449, 3,704,603, 3,760,948 and 3,815,386. While prior art structures have been generally successful and practical in performing such treatments, problems of fatigue of the prior art apparatus have been encountered, resulting both from the constant up and down movement imparted to the screen-assemblies in the prior art (to dislodge pulp sticking to the screens) and the non-synchronous operation of hydraulic cylinders or the like for performing such up and down movement, and problems of uneven treatment of the pulp have been encountered in large vessels and where a large volume of pulp per unit time is being treated.
According to the present invention, failure of the component parts due to fatigue of the strainer assembly is avoided despite constant up and down movement thereof, and even treatment of the pulp with bleaching or washing liquid or the like is provided even in large vessels and for large pulp volumes per unit time. According to the present invention, each of the ring-like concentric screens is connected to a ring-like header, side plates of the screen and header being disposed in end-to-end relationship. The header plates are solid and spaced about the same radial distance as the screen plates are spaced. Means, such as a perforated rigid ring member having substantially the same width as the distance between screen plates, are provided for connecting each header and screen together in fluid communicating relationship. Means for providing torsional and bending stiffness and for providing fluid communication are also provided for attaching each header to radially extending arms of the assembly. These means include a pair of torsion bars forming part of the header, one disposed on either side of spaced side plates of the arm, and means (i.e. welds) for connecting the torsion bars to top and bottom portions of the arm. Perforations formed in the torsion bars and in the arm side plates adjacent thereto are provided for providing fluid communication between the arms and headers.
According to the present invention, only three radially extending arms and axial movement actuators therefor need be provided for support and movement of the assemblies, rather than a larger number which are often necessary in prior art devices. The provision of three radially extending arms minimizes the stresses that may be imparted to the assembly as the result of slightly non-synchronous operation of the hydraulic cylinders associated with arm. Also, more uniform pulp treatment is provided since liquid passing through a screen may flow directly downwardly (or upwardly) from any point therealong, rather than being forced to first travel arcuately--the effect of pressure differential provided along the arcuate lengths of the screens results in flow of liquid more uniform according to the present invention because of the provision of the headers.
It is the primary object of the present invention to provide an improved cellulose pulp or the like treatment assembly for large volume vessels and high volume/unit time treatment. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.